Recently, as the tall buildings and the interior space become complicated, the shadow area with a poor radio wave environment in a wireless communication system occurs in all over the building. In addition, in the case of a vehicle, since a vehicle body is entirely made of a metal, a transmission/reception rate of a radio wave is lowered.
As a technique for solving such a problem, a relay is used to improve a poor radio wave environment. The technique using the relay improves a radio wave environment by employing an active relay which uses two antennas and a bidirectional amplification circuit therebetween or a passive relay which connects two antennas through a coaxial cable or a waveguide. More specifically, an antenna is installed outside a building or a vehicle, and the antenna is connected to a re-radiation antenna installed inside the building or the vehicle through a waveguide or a coaxial cable, thereby improving a radio wave environment in a shadow area.
However, since a conventional relay requires a coupler, a band pass filter, and a detection element for each of a plurality of frequency bands so as to confirm a frequency band of a communication signal received from a user device or the like, the conventional relay has a large circuit volume, is expensive, and has low power efficiency.
Therefore, there is a need to develop a communication apparatus for detecting a frequency band without causing such a problem.